These are data about soil carbon and nitrogen content in various forests around the upper valley. I chose sites based on the tree species that grew there– one of six target species needed to dominate (>60% BA) the plot. I looked for each tree species in multiple sites to make sure I wasn’t confusing site effects from tree species effects. The species were chosen to span a range of litter qualities (for now, calling these “Low”, “Medium” and “High”) and mycorrhizal associations (AM & ECM).
There were some outliers in here that Caitlin suggested I remove. One spot possibly experienced a fire in the past, she thought.
The three soil fractions are “free light” material, “occluded light” material, and “heavy” material. Free light material is mostly intact leaves, roots, and other organic material. It is the least decomposed. This stuff is going to decompose eventually, so we can think of it as a pool that is vulnerable to mineralization (being passed through microbes and made into inorganic matter, like CO2). It’s called “light” because it is not dense, and floats in a solution of heavy liquid. Occluded light material is also “light” in the sense that it floats in a dense solution, but it is not “free”–it would not float to the top if you dunked a handful of soil into a bucket of water. Instead, this material is stuck inside soil aggregates, which are heavy enough not to come to the surface even though the material on it’s own would normally do so. It may also be stuck to some heavier material surfaces. We get it out by agitating the soil and then it floats to the top. Finally, everything that is left is the “heavy” fraction because it is mostly minerals like sand, silt and clay. It sinks in even a very dense liquid. A small amount of organic matter is stuck to these minerals and we can think of that material as being inaccessible to soil decomposers. They can’t break it free from the bonds that hold it to mineral surfaces, even with an input of energy. This stuff can remain in soil for centuries and is an important long-term sink that may not be vulnerable to mineralization, even with changing soil moisture and temperature.